Application of nitride semiconductors to semiconductor devices with high withstand voltage and high power has been studied utilizing characteristics such as high saturated electron velocity and wide band gap. For semiconductor devices using nitride semiconductors, there have been many reports on field effect transistors, particularly high electron mobility transistors (HEMTs).
For example, in GaN-based HEMTs (GaN-HEMT), an InAlN-HEMT using GaN as a channel layer and InAlN as a barrier layer attracts attention. InAlN is known to lattice match with GaN in an In composition range of 17% to 18%. In this composition range, InAlN has a very high spontaneous polarization so as to implement two-dimensional electron gas (2DEG) with higher concentration than conventional AlGaN-HEMT. Therefore, InAlN/GaN-HEMT has attracted attention as a next generation high power device.